TW201428111A - Ferritic stainless steel having excellent antibacterial activity and method for manufacturing the same - Google Patents

Abstract

A first aspect of this ferritic stainless steel includes, in terms of percent by mass, Cu: 0.1% to 5.0%, and has a Cu concentrated layer on a surface, wherein a Cu maximum concentration Cm in the Cu concentrated layer is in a range of 10.0 mass% or more, and a ratio of Fe/Cr at a depth position from the surface where the Cu maximum concentration Cm is obtained is in a range of 2.4 or more. A second aspect of this ferritic stainless steel includes, in terms of percent by mass, Cu: 0.1% to 5.0%, and has a Cu concentrated layer on a surface, wherein a Cu maximum concentration Cm in the Cu concentrated layer is in a range of 18.0 mass% or more.

Description

Fertilizer iron-based stainless steel plate with excellent antibacterial property and manufacturing method thereof Technical field

The invention relates to an iron-based stainless steel plate with excellent antibacterial property and a manufacturing method thereof. More specifically, it relates to a cock which is suitable as a guardrail, a faucet, a metal coin, a metal container, a metal food device, a bathtub, A ferrite-based iron-based stainless steel sheet of a sanitary appliance such as a household appliance, a toilet, a medical appliance, a heater, or the like, and a building material, and a method of manufacturing the same.

The present application claims priority based on Japanese Patent Application No. 2012-282843, filed on Dec. 26, 2012, and the Japanese Patent Application No. 2013-148950, filed on Jan. 17, 2013. content.

Background technique

Fertilizer iron-based stainless steel sheets have been widely used in home appliances such as kitchen equipment and microwave side panels around the sink. Recently, it has also been used in indoor appliances such as bathroom basins and medical appliances such as guardrails to meet the needs of cleanliness, design and aesthetics. That is, the use of stainless steel sheets in places where bacteria are susceptible to growth and where no bacteria are allowed to grow has begun to increase. In addition, in recent years, concerns about the adverse effects of the above-mentioned germs on the human body have deepened. The tendency, especially for medical equipment and kitchen equipment requiring cleanliness, or the building materials for building buildings, has increased the antibacterial requirements. From the above, the development of the antibacterial property of the ferrite-grained stainless steel sheet itself used for the parts requiring such cleanliness has been carried out.

The above-mentioned research and development can be exemplified by Patent Document 1 and Patent Document 2. There has been disclosed a technique of imparting antibacterial properties by coating a resin mixed with an antibacterial agent on a stainless steel surface or by performing a plating method containing an antibacterial component in a matrix.

Further, Patent Document 3 to Patent Document 5 are also known as methods for providing the stainless steel material itself with antibacterial properties. Patent Document 3 and Patent Document 4 apply a positive potential to a Cu-containing ferrite-based iron-based stainless steel material and a Worthite iron-based stainless steel material by an AC electrolytic treatment method to dissolve Cu from the electrolytic solution, and then apply a negative potential to Cu. It is deposited on the surface of stainless steel to make it antibacterial.

Further, Patent Document 5 polishes and grinds the surface of the ferrite-containing iron-based stainless steel material containing Cu and the surface of the Worthian iron-based stainless steel plate and the maitian iron-based stainless steel plate, followed by glow annealing or nitric-hydrofluoric. The acid is pickled, and a layer in which Cu has been concentrated to 3% by mass or more is formed on the steel surface layer.

Further, recently, antibacterial stainless steel has been used in various applications. For example, metal coins are mostly made of ferrite-based iron-based stainless steel because of their good workability and low cost efficiency. The low-cost raw material iron-based stainless steel has an economic advantage.

When the ferrite-based iron-based stainless steel is applied to a metal coin or the like, it is required to be softened to a degree such as Hv190 because perforation and imprintability are required. In particular, in order to impart antibacterial properties, the iron-containing stainless steel containing Cu has solid solution strengthening and precipitation. Strengthen the hardening problem caused by it.

For example, Patent Document 6 discloses a Hv hardness of a ferrite-based iron-based stainless steel containing 0.66% or more of Cu. For example, when Hv is 171 and 13.57Cr-1.08Cu at 16.87Cr-0.66Cu, the Hv is 166.

Further, in Patent Document 7, a method for producing a ferrite-containing iron-based stainless steel containing Cu is proposed to be cooled to a coiling temperature of 500 to 300 ° C after hot rolling by a cooling rate after hot rolling at 3 ° C/s or more. In order to control the Cu grouping existing in the hot-rolled sheet to a maximum of 5 nm or less, and to avoid the technique of poor toughness.

However, as proposed in Patent Document 1 and Patent Document 2, when a resin mixed with an antibacterial agent is applied to the surface or a plating layer containing an antibacterial component is formed, the surface gloss characteristic of the stainless steel is lost. Therefore, it will detract from its commercial value in terms of the use of surface gloss. Further, the antibacterial resin film and the plating layer containing the antibacterial component are likely to be broken and not damaged at the time of press working and use. Moreover, the antibacterial component will dissolve in a humid environment, deteriorating the appearance, and losing the original antibacterial effect.

Further, Patent Document 3 to Patent Document 5, which can provide antibacterial properties to the stainless steel material itself, are disadvantageous. That is, the AC electrolytic treatment method disclosed in Patent Document 3 and Patent Document 4 is to deposit Cu on the surface of stainless steel by electroplating. Therefore, Cu is easily peeled off from the surface of the steel, such as a friction surface such as a wire brush or a steel brush, so that the surface of the Cu can be scraped off, and the antibacterial property is lowered.

In addition, the inventors of the present invention have reviewed a conventional technique in which the surface Cu concentration is controlled to a certain value or more to obtain an antibacterial property. As a result, it has been found that these conventional techniques may have a large deviation in antibacterial property in the direction of the plate width in the same plate surface. That is, conventional techniques have been discovered The antibacterial stainless steel obtained by the method has a good antibacterial property and a poor antibacterial property in the surface of the plate, and when the antibacterial product is produced, the yield is lowered.

As described above, the technique which has been disclosed so far that the stainless steel itself has an antibacterial property has a problem that the antibacterial property is easily lowered or the yield is poor.

In addition, when the ferrite iron-based stainless steel sheet is also required to be softened, the hardness must be controlled. The above-mentioned conventional techniques for hardness have the following problems.

The ferrite-based iron-based stainless steel disclosed in Patent Document 6 has a Cu concentration of 0.66 to 1.08% and a Hv of 190 or less. However, the ferrite-based stainless steel disclosed in Patent Document 6 does not satisfy the formula (a) of the present invention to be described later, and when high corrosion resistance is required in addition to softening, the condition cannot be satisfied.

Patent Document 7 specifies that the cooling rate after hot rolling to coiling is 3° C./s or more, and the Cu group is controlled to be 5 nm or less to improve the toughness. However, techniques for softening cold rolled materials have not been disclosed.

As described above, the technique of considering both antibacterial property and softening of the iron-containing stainless steel containing Cu fertilizer has not been disclosed.

Advanced technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 5-228202

Patent Document 2: Japanese Patent Laid-Open No. Hei 6-10191

Patent Document 3: Japanese Patent Laid-Open No. Hei 8-60302

Patent Document 4: Japanese Patent Laid-Open No. Hei 8-60303

Patent Document 5: Japanese Patent Laid-Open No. Hei 11-172380

Patent Document 6: Japanese Patent Laid-Open Publication No. 2003-213378

Patent Document 7: International Publication No. 2012/108479

Summary of invention

An object of the present invention is to provide a ferrite-based iron-based stainless steel sheet which can achieve both antibacterial property and softening, and a method for producing the same.

In order to solve the above problem of the antibacterial property, the inventors of the present invention have made efforts to review the difference between the antibacterial portion and the antibacterial portion in the panel. The result was the following findings.

(i) In order to have antibacterial properties, the minimum concentration of Cu in the Cu-concentrated layer on the steel surface must be 10% by mass or more.

(ii) Further, it has been found that the Cu concentration control on the steel surface is necessary for the antibacterial property, but it is not sufficient. In other words, according to the evaluation results of the inventors of the present invention, even when the maximum Cu concentration on the steel surface is 10% by mass or more, the antibacterial property is poor. This represents a factor in the production of antibacterial properties in addition to the maximum concentration of Cu on the steel surface. It has been speculated that due to the fact that these factors have not been grasped so far, there is a great antibacterial deviation in the board surface. Therefore, the inventors of the present invention have further expanded the investigation into the composition of the steel surface layer portion in order to find out the above factors. As a result, it was found that the antibacterial property was strongly correlated with the existence state of Fe and Cr which are main components of the Cu-concentrated layer on the steel surface. Cu in the Cu-concentrated layer on the steel surface can be evaluated as a factor of left and right antibacterial property. However, since the Cu is dissolved from the surface of the steel to inhibit the cell activity of the bacteria, it is antibacterial. Therefore, it has been assumed that the relationship between Fe and Cr existing in the vicinity of Cu in the Cu-concentrated layer is antibacterial. The impact is great. It was found that the antibacterial property was obtained for stability, and the Fe/Cr ratio was controlled in addition to the maximum Cu concentration of the Cu-concentrated layer known so far.

(iii) Further, according to the evaluation results of the present inventors, if the maximum Cu concentration on the steel surface is 18% by mass or more, even if the Fe/Cr ratio is not controlled, no antibacterial property is found. Ample antibacterial properties are obtained.

Further, in order to soften the above-mentioned antibacterial material (steel sheet), the inventors of the present invention further evaluated the effect of heat treatment on the hardness of the Cu-containing iron-based stainless steel sheet. Specifically, a review was made on the solid solution of Cu, the form of precipitation, and the heat treatment (heating and cooling conditions) which affected it, and the following findings were obtained.

(a) A very large difference in the precipitation form of Cu has been found by comparing the structure of a hard material with a soft material. Fine Cu particles of 10 to 100 nm have been observed in hard materials. However, almost no precipitation of Cu was observed in the soft material. Although the soft material Cu is solidly dissolved in the ferrite iron, the hardening value due to solid solution strengthening is small. Therefore, the main factor of inferior hardening is derived from the precipitation strengthening of Cu, and the inhibition of precipitation contributes to softening.

Further, the size of the above Cu precipitates was on the order of nm scale, and the structure was observed using a TEM (transmission electron microscope) to which the microstructure of the microdomain was applied. The sample was adjusted by a electrolytic polishing method to form a film sample, and was expanded to a maximum of 200,000 times by TEM to observe it, and Cu precipitates were observed.

(b) It is softened by precipitation inhibition of Cu, and it has been found that the heat treatment conditions which contribute to softening based on the iron-based stainless steel containing 1.5% of Cu (the following (b-1), b-2)) . Further, the above heat treatment conditions are similar to Cu: 0.3 to 1.7% by mass of the ferrite-based iron-based stainless steel which contributes to softening as well.

(b-1) It has been found that when the final annealing is performed, the solution temperature is 900 to 1100 ° C, and after cooling to less than 500 ° C, the softening can be performed by satisfying the following formula (a) of the hardness Hv. The solid solution temperature of 900 to 1100 ° C allows Cu to precipitate and then dissolve, and it can be inferred to contribute to softening. Moreover, an average cooling rate of 3 ° C / s or more can also suppress Cu precipitation.

Hv≦40×(Cu-0.3)+135...(a)

Further, Cu in the formula represents a Cu content (% by mass).

On the other hand, when the above formula (a) is not satisfied, a high-density Cu precipitate can be observed in the steel. Even if it softens to below Hv190, the corrosion of Cu precipitated in this way is inferior.

(b-2) When the hot rolled sheet is annealed, continuous annealing is performed instead of batch annealing in view of suppressing Cu deposition, and is heated to 800 to 1100 ° C, and then cooled to 400 at an average cooling rate of 1 ° C / s or more. °C. Thereby, softening can be performed within the range of the above formula (a) which satisfies the hardness prescribed by the present invention.

Further, the Cu precipitates specified in the present invention are almost extremely small, and the coarse precipitates of about 10 to 1000 nm are only partially present. Further, although the conventional technique controls the Cu precipitates to improve the antibacterial property and the high-temperature characteristics, the size thereof is almost 10 to 1000 nm, and the precipitation density is extremely high.

The present invention has been conceived based on the above findings, and its contents are as follows.

(1) A ferrite-based iron-based stainless steel sheet having excellent antibacterial properties, which contains 0.1% or more and 5.0% or less by mass of Cu, and a Cu-concentrated layer on the surface of the stainless steel sheet, Cu of the Cu-concentrated layer The maximum concentration Cm is 10.0% by mass or more, and the surface of the steel sheet exhibiting the aforementioned maximum Cu concentration Cm is in the depth position. The upper Fe/Cr ratio is 2.4 or more.

(2) A ferrite-based iron-based stainless steel sheet having excellent antibacterial properties, which contains 0.1% or more and 5.0% or less by mass of Cu, and a Cu-concentrated layer on the surface of the stainless steel sheet, Cu of the Cu-concentrated layer The maximum concentration Cm is 18.0% by mass or more.

(3) The ferrite-based iron-based stainless steel sheet having excellent antibacterial property as described in the above (1) or (2), wherein the content of the aforementioned Cu is 0.3 to 1.7% by mass%, and the section hardness of the steel sheet is in accordance with the Vickers hardness standard. The meter satisfies the following formula (a).

Hv hardness ≦ 40 × (Cu-0.3) + 135... (a)

(4) The ferrite-based iron-based stainless steel sheet having excellent antibacterial property according to any one of the above (1) to (3), further comprising, by mass%: C: 0.050% or less, Cr: 10.0 to 30.0%, Si: 2.00% or less, P: 0.030% or less, S: 0.010% or less, Mn: 2.00% or less, N: 0.050% or less, and Ni: 2.0% or less, and the remainder is composed of Fe and unavoidable impurities.

(5) The ferrite-based iron-based stainless steel sheet having excellent antibacterial properties as described in the above (4), which further contains one or both of Ti: 0.50% or less and Nb: 1.00% or less in terms of % by mass.

(6) The ferrite-based iron-based stainless steel sheet having an excellent antibacterial property according to the above (4) or (5), which further contains at least one selected from the group consisting of Sn: 1.00% or less, and Mo: 1.00% or less, Al: 1.000% or less, Mg: 0.010% or less, Co: 1.000% or less, V: 0.50% or less, Zr: 0.10% or less, REM: 0.100% or less, La: 0.100% or less, B: 0.0100% The following and Ca: 0.010% or less.

(7) A ferrite-based iron system having excellent antibacterial properties as described in any one of the above (1) to (6) Stainless steel plate, which is used for metal coins.

(8) A method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial property, comprising a hot rolling step, a cold rolling step, and a final pickling step; and the stainless steel sheet has the composition of any one of the above (1) to (6) And the first pickling step comprises the steps of: immersing in a 5.0 to 35.0% by mass aqueous sulfuric acid solution; and second absorbing step of immersing in 1.0 to 15.0% by mass of nitric acid; It is mixed with an aqueous solution of 0.5 to 5.0% by mass of a hydrofluoric acid aqueous solution.

(9) The method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial property as described in the above (8), wherein the hot rolling step is at a heating temperature of 1150 to 1300 ° C, a final temperature of 800 to 1000 ° C, and a coiling temperature of 600 ° C. Under the following conditions.

(10) The method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial property according to (8) or (9) above, further comprising a hot-rolled sheet annealing step and a final annealing step; wherein the stainless steel sheet has the above (3)~ (6) The composition of any one of the components; and the final annealing step comprises the steps of annealing at an annealing temperature of 900 to 1100 ° C; and cooling to 400 ° C at an average cooling rate of 3 ° C /sec or more.

(11) The method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial property as described in the above (10), wherein the hot-rolled sheet annealing step is performed by continuous annealing, and the continuous annealing comprises: annealing temperature of 800 to 1100 The step of annealing at ° C; secondly, the step of cooling to 400 ° C at an average cooling rate of 1 ° C/sec or more.

According to the present invention, the ferrite-rich iron-based stainless steel sheet excellent in antibacterial property and the method for producing the same can exhibit good antibacterial properties in the entire surface of the panel. Therefore, it is possible to achieve a better antibacterial property than before in a higher yield. Further, according to a preferred embodiment of the present invention, the maximum concentration of Cu on the steel surface can be highly concentrated to the extent that it has hitherto been first seen, whereby a more excellent antibacterial property can be obtained. Further, the Cu content of the ferrite-rich stainless steel is limited to 0.3 to 1.7%, and the conditions of annealing and final annealing of the hot-rolled sheet are controlled to sufficiently soften. Therefore, both softening and excellent antibacterial properties can be achieved. The ferrite-based iron-based stainless steel sheet of the present invention having such characteristics can be suitably used as a coin made of metal.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph exemplifying the concentration distribution of C, O and main elements in the depth direction of the stainless steel of the present invention.

Fig. 2 is a graph illustrating the concentration distribution of O and main elements in the depth direction of the stainless steel of the present invention.

Fig. 3 is a graph showing the relationship between Cu maximum concentration, Fe/Cr ratio, and antibacterial property evaluation in Examples (Inventive Examples) and Comparative Examples of the present invention.

Form for implementing the invention

Hereinafter, a ferrite-based iron-based stainless steel sheet having excellent antibacterial properties according to an embodiment of the present invention and a method for producing the same will be described in detail. In addition, unless otherwise noted, the content % of an element means mass %.

The ferrite-based stainless steel sheet according to the first embodiment contains 0.1% or more and 5.0% or less by mass of Cu, and has a Cu-concentrated layer on the surface of the stainless steel sheet, and the Cu maximum concentration Cm of the Cu-concentrated layer is 10.0 mass. More than %, and the surface of the steel sheet exhibiting the Cu maximum concentration Cm has a Fe/Cr ratio of 2.4 or more in the depth position.

In addition, the ferrite-based stainless steel sheet of the second embodiment contains 0.1% or more and 5.0% or less by mass of Cu, and has a Cu-concentrated layer on the surface of the stainless steel sheet, and the Cu maximum concentration Cm of the Cu-concentrated layer. It is a ferrite iron-based stainless steel plate of 18.0% by mass or more.

The ferrite-based stainless steel sheet according to the first embodiment or the second embodiment may further contain C: 0.050% or less, Cr: 10.0 to 30.0%, Si: 2.00% or less, and P: 0.030% or less, depending on the mass%, and S: 0.010% or less, Mn: 2.00% or less, N: 0.050% or less, and Ni: 2.0% or less.

The ferrite-based stainless steel sheet according to the first embodiment or the second embodiment may further contain one or both of Ti: 0.5% or less and Nb: 1.00% or less in terms of mass%.

The ferrite-based stainless steel sheet according to the first embodiment or the second embodiment may further contain Sn: 1.00% or less, Mo: 1.00% or less, Al: 1.000% or less, Mg: 0.010% or less, and Co: 1.000 by mass%. % or less, V: 0.50% or less, Zr: 0.10% or less, REM: 0.100% or less, La: 0.100% or less, B: 0.0100% or less, and Ca: 0.010% or less.

Here, the Cu-concentrated layer means a field in which the Cu concentration is higher than the average Cu concentration of the ferrite-based iron-based stainless steel sheet in the surface layer of the ferrite-based iron-based stainless steel sheet. Specifically, the ferrite-based stainless steel sheet of the present embodiment can be detected by glow discharge luminescence analysis (GDS), and the element which is concentrated to the surface by the pickling step and the element constituting the oxide are as high as about 800 nm from the surface of the steel sheet. Depth so far. The details of the detection elements are left to be described later. Once the concentration distribution of O, Fe, Cr, Si, Mn, Nb, Ti, Al, Cu is measured, the concentrations of Cu, Fe, and Cr will be The concentration distribution in the depth direction is exhibited as shown in FIG. In Fig. 2, the Cu concentration at a depth of 30 nm from the surface is larger than the Cu concentration at a depth exceeding 30 nm. In Fig. 2, if the Cu concentration exceeding the depth of 30 nm is the average Cu concentration of the stainless steel plate, the Cu-concentrated layer of Fig. 2 is the field from the surface to the depth of 30 nm. The Cu-concentrated layer can be determined as described above.

Further, the Cu concentration determined by GDS analysis is represented by the concentration of Cu in terms of the total amount of O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu. In the Cu-concentrated layer, the concentration at which the Cu concentration is the largest is the Cu maximum concentration Cm. Further, the ratio of the Fe concentration to the Cr concentration at the depth of the Cu maximum concentration Cm from the surface of the steel sheet is referred to as the Fe/Cr ratio in the present embodiment. In the example of Fig. 2, the Cu maximum concentration Cm was 75.0%, and the Fe/Cr ratio was 2.9.

O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu are concentrated to the elements of the surface and the elements constituting the oxide by the pickling step, and are therefore used for calculation of Cu concentration.

Further, P, S, N, and Ni are not concentrated to the surface or constitute an oxide in the pickling step and are concentrated to the surface, so the calculation of the Cu concentration is not considered.

Ti, Nb, and Al are optional elements of the present embodiment, but are elements constituting an oxide. Therefore, the calculation of the Cu concentration will be considered. When these elements are not contained, the Cu concentration is calculated by the concentration of these elements being 0%.

Further, since C is a pollution element, it is measured by GDS analysis, and C is excluded to calculate the Cu concentration.

Hereinafter, the Cu content of the ferrite-based iron-based stainless steel sheet will be described.

Cu is the most important element for improving the antibacterial property in the ferrite-based stainless steel sheet of the embodiment. In the present embodiment, the Cu maximum concentration Cm of the Cu-concentrated layer must be 10.0% or more. When the Cu content of the steel is less than 0.1%, the Cm value of 10.0% or more cannot be achieved even if the production method of the present embodiment described later is applied. Therefore, the lower limit of the Cu content of steel is set to 0.1%. On the other hand, if the Cu content is too large, cracking of the cast piece occurs during the production process, so the upper limit is made 5.0% or less. The Cu content of steel should be 0.1~1.7%, and 0.2~1.5% is the best.

In the present embodiment, the antibacterial property is achieved, and the element distribution of the steel surface layer must be strictly controlled. First, the Cu maximum concentration Cm of the Cu-concentrated layer on the steel surface must be 10.0% or more. When it is less than 10.0%, the antibacterial property cannot be achieved even if other regulations are satisfied. The Cu maximum concentration Cm is preferably 11.0% or more, and more preferably 18.0% or more. In addition, even if the Cu maximum concentration Cm is greatly increased, the antibacterial property is not adversely affected, so the upper limit is not specified.

Further, the relationship between the various antibacterial properties and the steel surface state was examined. As a result, it was found that the existence state of Fe and Cr which are main components of the Cu-concentrated layer of the steel surface layer must be appropriately controlled in accordance with the Cu maximum concentration Cm. Therefore, the Cu maximum concentration Cm and the Fe/Cr ratio will be described with reference to the graph of Fig. 3 .

Fig. 3 is a data showing the maximum Cu concentration Cm: 5 to 40% by mass and the Fe/Cr ratio: 1 to 6 in the data of Test Nos. 1 to 551 in Tables 2 to 15 of the examples to be described later. The main sample was sampled and plotted, and a graph showing the relationship between the Cu maximum concentration Cm, the Fe/Cr ratio, and the antibacterial evaluation was shown. The white circled drawing point in the graph of Fig. 3 represents an example in which the antibacterial property is good (invention example), and the black circular drawing point represents an example in which the antibacterial property is particularly good (invention example), the multiplication symbol (cross) Marked points of the mark) represent poor antibacterial properties Example (comparative example).

(A) When the Cu maximum concentration Cm is 10.0% or more and less than 18.0% (the stainless steel sheet of the first embodiment)

In the ferrite-based stainless steel sheet of the first embodiment, the Fe/Cr ratio must be 2.4 or more. As shown in Fig. 3, if the Fe/Cr ratio is less than 2.4, the antibacterial property cannot be achieved even if the Cu maximum concentration Cm is 10.0% or more. The reason for this is not clear, but the inventors of the present invention presumed that the combination of Fe and Cr may be unstable due to the Fe/Cr ratio of 2.4 or more, and the Cu in the Cu-concentrated layer may be unstable. Cu is less susceptible to oxidation than Fe and Cr at room temperature, that is, it is an element that is difficult to combine with oxygen. In the unstable state of Fe and Cr, the oxygen originally combined with Fe or Cr will be out of the bonded state, and the amount of oxygen around the Cu is increased. Therefore, it can be inferred that Cu, which is difficult to combine with oxygen, will easily dissolve from the surface of steel into water and become ions. Cu which is dissolved into ions can inhibit the cell activity of bacteria and thus produce antibacterial properties. Therefore, it is inferred that the antibacterial property is caused by making the Fe/Cr ratio of the steel surface layer within the above range. The Fe/Cr ratio is preferably 2.6 or more and 9.5 or less, and more preferably 3.0 or more and 9.0 or less. Further, in order to increase the Cu maximum concentration Cm to 10.0% or more and the Fe/Cr ratio to 2.4 or more, it is possible to control the pickling conditions in the production method of the present embodiment to be described later.

(B) When the Cu maximum concentration Cm is 18.0% or more (the stainless steel sheet of the second embodiment)

In the ferrite-grained stainless steel sheets of the first embodiment and the second embodiment, the Cu maximum concentration Cm can be increased to further improve the antibacterial property. Specifically, as in the case of the ferrite-based stainless steel sheet of the second embodiment, the Cu maximum concentration Cm is controlled to 18.0% or more, whereby the antibacterial property can be further improved. From the chart in Figure 3 It is understood that when the maximum Cu concentration Cm is higher than 18.0%, the Fe/Cr ratio is not particularly controlled. The reason for this is unknown. However, the inventors of the present invention have estimated that if the Cu maximum concentration Cm is 18.0% or more, the Cu concentration of the Cu-concentrated layer of the steel surface layer is increased, but the Fe concentration and the Cr concentration are lowered. Therefore, it is inferred that it is caused by a decrease in the influence of Fe and Cr in the Cu-concentrated layer. Therefore, it is presumed that regardless of the Fe/Cr ratio, Cu due to the Cu-concentrated layer is dissolved in water from the surface of the steel to become ions, and the cell activity of the bacteria is inhibited, whereby the antibacterial property is generated.

Further, in order to increase the Cu maximum concentration Cm by 18.0% or more, it is possible to control the pickling conditions and the rolling conditions in the production method of the present embodiment to be described later. Further, if the steel surface layer contains too much Fe, the corrosion resistance of the ferrite-based iron-based stainless steel sheet is lowered, so Fe/Cr is preferably made 10.0 or less. However, if the amount of Fe contained in the steel surface layer is too small, a large amount of Cr is formed on the surface of the steel to be easily oxidized, so it is preferable to make Fe/Cr 0.4 or more. Fe/Cr should be 0.4~10.0, and 0.5~9.5 is better.

(softening of ferrite iron-based stainless steel sheet)

As described above, in addition to controlling the surface of the steel to achieve antibacterial properties, it is also required to perform softening, and final annealing contributes to the suppression of Cu precipitation. Hereinafter, specific conditions and the like for softening the ferrite-grained stainless steel sheet of the first embodiment and the second embodiment will be described.

First, in order to achieve both antibacterial and softening, it is preferred to have a Cu content of 0.3 to 1.7%. If the Cu content is less than 0.3%, it is much lower than the solid solubility limit of Cu, so hardening due to precipitation of Cu hardly occurs. On the other hand, when the C content exceeds 1.7%, even if Cu precipitation is suppressed, the hardening value due to solid solution strengthening of Cu is also large, so that softening as defined in the present embodiment may be difficult to achieve.

The precipitation form of Cu is also affected by the Cu content and the like, and is a granular or rod shape of 10 to 100 nm. In the hard stainless steel plate, although the size of the Cu precipitate is not uniform, the Cu precipitation density is large. In addition, in the soft stainless steel plate, the precipitation density of Cu is small, and the precipitation size is also small. Therefore, it has been inferred that Cu precipitation is a major factor in hardening. For confirmation, a hard stainless steel plate was used as a material and subjected to reheat treatment under the conditions specified in the present embodiment, and the microstructure before and after the heat treatment was compared. As a result, it has been found that even if the components are the same, the Cu precipitation density of the soft material is small and the Cu precipitation size is small as compared with the hard material.

Further, the above-described control for the precipitation of Cu for softening is focused on re-dissolving Cu and not depositing Cu as much as possible during the cooling process. The related factors include the solid solution temperature and the cooling rate, and are manufactured according to the annealing conditions of the hot rolled sheet and the final annealing conditions described later, and the softening effect has been achieved.

The cross-sectional hardness of the soft stainless steel sheet of the present embodiment can satisfy the following formula (a) according to the Vickers hardness scale. In addition, the formula (a) has been derived as explained below. The results of various Vickers hardness measurements have been plotted on a graph centered on Cu concentration and Vickers hardness. Then, according to the corrosion resistance classification, the point after the plot. As a result, the formula (a) has been derived as a range in which the Vickers hardness (Hv hardness, or Hv) is 190 or less and also has corrosion resistance. When the formula (a) is not satisfied, even if the Hv is 190 or less, it is soft and the corrosion resistance is inferior. This is presumably due to excessive precipitation of Cu.

Hv hardness ≦ 40 × (Cu-0.3) + 135... (a)

Further, "Cu" in the formula (a) represents a Cu content (% by mass).

Hereinafter, other chemical components of the ferrite-based stainless steel sheet of the first embodiment and the second embodiment will be described. The essential features of this embodiment are as follows The above is the control of the element concentration distribution of the steel sheet surface layer. In the following, the composition of the steel which can be used in consideration of factors other than the antibacterial property such as corrosion resistance, workability, and manufacturability is also disclosed. However, the composition of the antibacterial stainless steel sheet to solve the problem of the present invention is not limited. In the following ingredients.

C is an impurity element which is inevitably mixed with a self-dissolving raw material, and the amount thereof is preferably small and does not have a lower limit. When the amount of C exceeds 0.050%, the toughness and cold workability of steel are deteriorated, so the upper limit can be made 0.050% or less. The amount of C is preferably 0.040% or less, and more preferably 0.020% or less. Further, excessive reduction of the amount of C leads to an increase in manufacturing cost, so the amount of C should preferably be 0.001% or more.

Cr must be added in an amount of 10.0% or more to improve corrosion resistance and high temperature oxidation resistance. On the other hand, when the amount of Cr exceeds 30.0%, the formability may be deteriorated, so that the amount of Cr may be in the range of 10.0 to 30.0%. The amount of Cr is preferably from 12.0 to 27.0%, and the optimum is from 13.0 to 25.0%.

Si acts as a deoxidizing element and enhances high temperature oxidation resistance. In order to achieve the above effects, the content of Si may be made 0.01% or more. However, if a large amount of Si is added, the steel sheet may be hardened to deteriorate ductility. Therefore, the Si content can be made 2.00% or less. The amount of Si is preferably from 0.01 to 1.50%, and more preferably from 0.10 to 1.20%.

P is an element that cannot be avoided from the raw material. P is a grain boundary segregation element. If the content is too large, the cold workability and toughness of the steel sheet are deteriorated, so that the amount of P can be made 0.030% or less.

S and P are the same elements that cannot be avoided from the raw material. S is an element which deteriorates corrosion resistance and moldability, so the amount of S can be made 0.010% or less.

Mn acts as a deoxidizer. And it can prevent S to grain boundary Grain boundary embrittlement caused by segregation. In order to achieve such effects, the Mn content can be made 0.10% or more. However, too much content will lower the cold workability of the steel sheet. Therefore, the Mn content can be made 2.00% or less. The amount of Mn is preferably 0.10 to 1.80%, and more preferably 0.12 to 1.50%.

When the content of N is large, the formability is deteriorated, so it can be 0.050% or less. The amount of N is preferably 0.040% or less, and more preferably 0.030% or less. In addition, excessive reduction of the amount of N will result in an increase in manufacturing cost, so the amount of N should preferably be 0.001% or more.

Ni can improve the hot workability of the ferrite-based stainless steel sheet of the present embodiment. In order to obtain this effect, the content of Ni can be made 0.1% or more. However, if the Ni content is excessive, the stability of the ferrite iron is lowered, so that the amount of Ni can be made 2.0% or less. The amount of Ni is preferably 1.5% or less, and more preferably 1.2% or less.

In addition to the above-described component elements, the fat-grained iron-based stainless steel sheets of the first embodiment and the second embodiment are composed of Fe and impurities which are inevitably mixed.

Further, in the ferrite-based stainless steel sheet of the first embodiment and the second embodiment, Ti and Nb may be further contained as an optional component. Since Ti and Nb are carbonitride-forming elements, they are elements which can improve formability. Therefore, either or both of Ti and Nb may be contained as needed. In order to obtain the effect of improving the formability, it may contain 0.002% or more of Ti and 0.002% or more of Nb. However, excessive addition of Ti and Nb leads to deterioration of workability and reduction in toughness. Therefore, when it is contained, it is preferable to set Ti: 0.50% or less and Nb: 1.00% or less. Ti: 0.45% or less, Nb: 0.95% or less, Ti: 0.40% or less, and Nb: 0.90% or less is more preferable.

Further, in the first embodiment and the second embodiment, the ferrite is not The rust steel plate may contain one or more of the following elements as needed.

Sn is an element that contributes to the improvement of corrosion resistance. In order to obtain this effect, the content of Sn can be made 0.005% or more. However, if it exceeds 1.00%, the toughness is deteriorated, so the amount of Sn is made 1.00% or less. The amount of Sn is preferably 0.60% or less, and more preferably 0.50% or less.

Mo is an element that contributes to the improvement of corrosion resistance. In order to obtain this effect, the content of Mo may be made 0.002% or more. However, if it exceeds 1.00%, the toughness is deteriorated, so the amount of Mo is made 1.00% or less. The amount of Mo is preferably 0.70% or less, and more preferably 0.50% or less.

Al, like Mo, can play a role in improving corrosion resistance. In order to obtain this effect, the content of Al may be made 0.002% or more. However, if the content exceeds 1.000% and is excessive, the manufacturability and workability are lowered. The amount of Al is preferably 0.300% or less, more preferably 0.100% or less.

Mg can form a Mg oxide in molten iron to function as a deoxidizer. Further, Mg acts as a crystal nucleus of TiN and forms a fine ferrite iron phase upon solidification. By making the solidified structure finer, the surface defects of the steel sheet caused by the coarse solidification structure can be avoided, and the workability can be improved. Therefore, Mg may be contained as needed. In order to achieve the above effects, the Mg content may be 0.001% or more. However, if the content exceeds 0.010% and is excessive, the manufacturability and workability are lowered. The amount of Mg is preferably 0.009% or less, more preferably 0.008% or less.

Co is the same as Mo and can exhibit the effect of improving corrosion resistance. In order to obtain this effect, the content of Co may be made 0.002% or more. However, if the content exceeds 1.000% and is excessive, the alloy cost will increase and the manufacturability will drop. low. The amount of Co is preferably 0.400% or less, and more preferably 0.200% or less.

V can form carbonitrides and play a role in increasing the strength of the steel. In order to obtain this effect, the content of V can be made 0.002% or more. However, if the content exceeds 0.50% and is excessive, the manufacturability and workability are lowered. The amount of V is preferably 0.20% or less, more preferably 0.10% or less.

Zr is the same as V to form carbonitrides and serves to increase the strength of the steel. In order to obtain this effect, the content of Zr can be made 0.003% or more. However, if the content exceeds 0.10% and is excessive, the manufacturability and workability are lowered. The amount of Zr is preferably 0.08% or less, and more preferably 0.05% or less.

REM, La, B, and Ca are all elements that can affect the presence of S in steel, and may be contained as needed to improve hot workability. In order to achieve the above effects, the content may be REM: 0.003% or more, La: 0.002% or more, B: 0.0002% or more, and Ca: 0.002% or more. The upper limit of these elements is REM: 0.100% or less, La: 0.100% or less, B: 0.0100% or less, and Ca: 0.010% or less, and the upper limit is REM: 0.080% or less, La: 0.095% or less, and B: 0.0095%. Hereinafter, Ca: 0.009% or less is preferable, and each of REM: 0.050% or less, La: 0.050% or less, B: 0.0060% or less, and Ca: 0.007% or less is more preferable. Further, the term "REM" in the present embodiment means an element of Sc, Y and atomic sequence 58 to 71.

As described above, the ferrite-based stainless steel sheet of the present embodiment described above can be applied to a coin application requiring antibacterial properties. Further, in the case of the softened iron-based stainless steel sheet which is softened in the present embodiment, it is also applicable to the case where the use of the coin is more soft.

Hereinafter, the production of the ferrite-grained stainless steel of the present embodiment will be described. Method of making.

In the production of the ferrite-based stainless steel of the first embodiment, the stainless steel having the above-described composition is sequentially subjected to a hot rolling step, a cold rolling step, and a final pickling step. Here, in the final pickling step, the first pickling step of immersing in a 5.0 to 35.0% by mass aqueous sulfuric acid solution, and the acid containing 1.0 to 15.0% by mass of nitric acid and 0.5 to 5.0% by mass of hydrofluoric acid aqueous solution are performed. The second pickling step of immersion in the liquid. The first pickling step of immersing in the aqueous sulfuric acid solution and the second pickling step of immersing in the acid solution containing the aqueous solution of nitric acid and hydrofluoric acid may be carried out in the above order, or the order may be reversed.

Further, in the production of the ferrite-based stainless steel according to the second embodiment, in addition to the production conditions of the first embodiment, in the hot rolling step, the heating temperature is 1150 to 1300 ° C, and the final hot rolling temperature is 800 to 1000 ° C. Hot rolling is carried out under the conditions of a coiling temperature of 600 ° C or lower.

The reason why the surface of the stainless steel plate is pickled is to remove the rust film adhered by the heat treatment, and to preferentially pickle and dissolve Fe and Cr to increase the Cu concentration on the surface. Various acid solutions have been proposed for the above-mentioned acid. However, after the inventors of the present invention repeatedly conducted experiments, it was confirmed that a specific concentration of the sulfuric acid pickling step (first pickling step) and a specific concentration of the nitric acid-hydrofluoric acid pickling step (second pickling step) were performed. In the case, the efficiency of scale removal and the promotion of Cu concentration in the steel surface layer can be significantly improved as compared with the case of using other acid liquids. Moreover, at this time, the other surface characteristics described above can also be obtained, and the antibacterial property can be achieved. According to the manufacturing method of the present embodiment found above, it is possible to reliably obtain a stainless steel having excellent antibacterial properties.

The acid used for pickling must meet the following conditions. That is, sulfuric acid The concentration of the aqueous solution must be in the range of 5.0 to 35.0% by mass. When the concentration of the aqueous sulfuric acid solution is less than 5.0% by mass, the acid aqueous solution hardly undergoes the dissolution reaction of the scale and the steel, so that Cu may not be concentrated to the surface. On the other hand, when the concentration of the aqueous sulfuric acid solution exceeds 35.0% by mass, the dissolution reaction by the aqueous acid solution proceeds largely to cause significant unevenness due to dissolution. The above-mentioned degree of unevenness will result in a strip shape or an uneven appearance of the finished board to lower the product quality. Therefore, the concentration of the aqueous sulfuric acid solution is preferably 6.0 to 34.0% by mass, more preferably 8.0 to 33.0% by mass.

The nitric acid-hydrofluoric acid aqueous solution must have a nitric acid concentration of 1.0 to 15.0% by mass and a hydrofluoric acid concentration of 0.5 to 5.0% by mass. When the concentration of nitric acid is less than 1.0% by mass, the dissolution reaction is almost impossible as in the case of sulfuric acid, so that Cu cannot be concentrated to the surface. On the other hand, when the concentration of nitric acid exceeds 15.0% by mass, the dissolution reaction proceeds greatly and the product quality is lowered.

Further, hydrofluoric acid is not used for the same concentration as that of sulfuric acid and nitric acid, and is not suitable for an aqueous solution concentration of less than 0.5% by mass and more than 5.0% by mass.

The nitric acid concentration is preferably from 1.2 to 14.5% by mass, the hydrofluoric acid concentration is from 0.7 to 4.7 mass%, the nitric acid concentration is from 1.5 to 14.0% by mass, and the hydrofluoric acid concentration is from 0.9 to 4.5% by mass.

Moreover, the time of immersing the steel sheet in the acid solution can be considered as the Cu maximum concentration Cm and other physical properties of the Cu concentrated layer, and the sulfuric acid aqueous solution and the nitric acid-hydrofluoric acid aqueous solution are appropriately selected in the range of 10 to 1000 seconds. . Further, the temperature of each of the aqueous acid solutions is not limited in general conditions, and is not particularly limited. For example, it can be carried out in the range of 40 to 80 °C.

In addition, the manufacturing method of the embodiment is characterized in that it is found The final acid pickling of the aqueous sulfuric acid solution and the aqueous solution of nitric acid-hydrofluoric acid can strictly control the physical properties of the steel surface layer within the above range. Therefore, for example, the pickling order of the aqueous sulfuric acid solution and the aqueous solution of nitric acid-hydrofluoric acid can be reversed. In addition, in addition to the sulfuric acid aqueous solution and the nitric acid-hydrofluoric acid aqueous solution, the third pickling treatment and the fourth pickling treatment may be carried out in addition to the physical property range of the ferrite-based stainless steel sheet of the present embodiment.

Hereinafter, the hot rolling step will be described.

As a result of the review by the inventors of the present invention, it is known that the conditions of the hot rolling step are strictly controlled, and the surface layer Cu can be concentrated in the hot rolling stage. Therefore, it is known that the final pickling of the cold-rolled sheet in a state in which the surface layer Cu concentration has been concentrated during hot rolling can further increase the surface layer Cu concentration and further improve the antibacterial property.

Specifically, it is known that hot rolling is performed under the conditions of a heating temperature of 1,150 to 1,300 ° C, a final temperature of 800 to 1000 ° C, and a coiling temperature of 600 ° C or less, and then the final pickling is performed under the above conditions to obtain a Cu maximum concentration Cm. Increase to 18.0%.

In order to increase the maximum Cu concentration by pickling and trimming after the hot rolling step, it is important to increase the Cu concentration in the surface layer during the production of the hot rolled sheet and to have Cu present in the solid solution state. When the heating temperature is 1150 ° C or more, only a small amount of Cu precipitate remaining in the steel embryo can be re-dissolved in a usual holding time. However, if it exceeds 1300 ° C, surface defects and the like due to grain coarsening will also waste heating energy.

Hereinafter, the range of the final temperature and the coiling temperature will be described. When the ferrite-based iron-based stainless steel sheet of the present embodiment is produced by the manufacturing steps of the conventional hot-rolled sheet, the Cu contained in the steel is formed as Cu precipitates upon cooling. Therefore, steel The amount of Cu dissolved in the solid solution will decrease. In addition, it has been confirmed that the final temperature at the time of manufacture of the hot-rolled sheet is 800 to 1000 ° C, and the hot-rolled sheet is cooled rapidly by a usual equipment such as a water sprayer, and is taken up at a temperature of 600 ° C or lower, so that Cu deposition does not occur. Things. It is known that the hot-rolled stainless steel sheet obtained as described above can be obtained by a conventional pickling to obtain a cold-rolled sheet having a high Cu concentration, and it is known that the surface layer contains Cu by the acid washing specified above. The concentration Cm is 18.0% or more, and the first high-concentration Cu-rich ferrite-based stainless steel sheet.

Although the reason is not clear, the inventors of the present invention presumed that it should be inferred as follows. When the steel is heated at 1150~1300 °C, Fe and Cr which are easily oxidized compared with Cu will oxidize earlier. Therefore, unoxidized Cu remains under the scale, so the surface Cu concentration will also increase. Further, the final hot rolling temperature is 800 to 1000 ° C, and the coiling is performed in a state of 600 ° C or lower, and when the Cu precipitate temperature region is passed in a short time, Cu precipitation can be suppressed. Therefore, a hot-rolled stainless steel sheet having a high Cu concentration on the surface and no Cu precipitate can be produced.

Further, when the steel sheet temperature is 600 ° C or lower, the Cu diffusion rate in the steel is slowed down, and the formation of Cu precipitates is suppressed, but Cu precipitates are still formed for a long period of time, so that it is preferable to perform water injection winding after the final hot rolling. The steel coil is then water cooled.

The conditions of the hot rolling step are heating temperature: more than 1200 ° C, final temperature: over 800 ° C, coiling temperature: 600 ° C or less, preferably heating temperature: 1250 ~ 1300 ° C, final temperature: 900 ~ 1000 ° C, Coiling temperature: 500 ° C or less is optimal.

Further, the antibacterial stainless steel sheet of the present embodiment described above is subjected to a final annealing step after cold rolling at 900 to 1100 ° C. Annealing is carried out and cooled to 400 ° C at an average cooling rate of 3 ° C /sec or more to soften to the hardness specified in the present embodiment.

When the solution temperature (final annealing temperature) is equal to or higher than the temperature at which Cu can be solid-solved, the effect on hardness is small. Therefore, in order to grasp the influence of the solid solution temperature on the hardness, a solution heat treatment (final annealing) is performed at various temperatures in the range of 700 to 1100 ° C, and then water cooling is performed. As a result, at a solid solution temperature of 900 ° C or higher, the hardness did not change at all, and the influence on the hardness was less than Hv10.

Moreover, the average cooling rate at the time of cooling after the solution heat treatment is 3° C./sec or more, and the Hv hardness satisfying the following formula (a) defined in the present embodiment can be formed and softened.

Hv hardness ≦ 40 × (Cu-0.3) + 135... (a)

In order to grasp the effect of the average cooling rate on the hardness, the solution heat treatment is performed at 900 to 1100 ° C, and then cooled by various cooling methods. As a result, it is known that it can be softened by cooling to a cooling end temperature to be described later at an average cooling rate of 3 ° C /sec or more. The average cooling rate of 3 ° C / sec or more can be controlled by a conventional device such as a blower, and the faster the cooling rate, the more the tendency to suppress the precipitation of Cu is, and the softening is facilitated. Therefore, the upper limit of the average cooling rate is not particularly set, and can be appropriately determined in consideration of the function of the cooling device to be used and the like.

At the time of cooling after the solution heat treatment, the cooling end temperature is 400 ° C or lower.

In order to grasp the effect of the cooling end temperature on the hardness, after the solution heat treatment at 900 to 1100 ° C, it has been cooled at an average cooling rate of 3 ° C / sec or more. It is controlled and cooled to various temperatures, and then naturally cooled (average cooling rate is less than 3 ° C / sec). As a result, when the cooling completion temperature is 400 ° C or lower, the Hv hardness of the above formula (a) which is defined in the present embodiment can be softened.

In addition, it has been confirmed that if the cooling end temperature is 500 to 700 ° C, significant hardening will occur. A Cu precipitate of 10 to 100 nm has been observed in the above hardened sample. Therefore, it is inferred that the temperature region of 500 to 700 ° C is the nasal temperature region where Cu is precipitated, and the nose temperature is rapidly precipitated by the above Cu, that is, the cooling rate is increased, which contributes to softening.

As described above, in the final annealing step of the present embodiment, the heating temperature (final annealing temperature): 910 to 1080 ° C, the cooling end temperature: 390 ° C or lower, and the average cooling rate: 3.2 ° C / sec or more are preferable. The heating temperature is 920 to 1060 ° C, the cooling end temperature is 380 ° C or lower, and the average cooling rate is 3.5 ° C / sec or more.

In order to soften and further define the annealing conditions of the hot rolled sheet after hot rolling, it is more advantageous in terms of suppression of Cu precipitation.

The annealing conditions of the hot rolled sheet are specified, and the size of the Cu precipitate can be controlled to the size at which solid solution can be performed in the final annealing of the subsequent step. In addition, hot-rolled sheet annealing is performed by continuous annealing, is not batch annealing, and is heated to 800 to 1100 ° C, and then cooled to 400 ° C at an average cooling rate of 1 ° C / sec or more.

If the heating temperature is less than 800 ° C, recrystallization will be insufficient. Further, when the temperature exceeds 1100 ° C, the crystal grains will be coarsely granulated, so that the subsequent manufacturability will be impaired. Further, the cooling end temperature was set to 400 ° C to suppress precipitation of Cu. The average cooling rate of 1 ° C / sec or less causes coarse precipitation of Cu precipitates, and also causes the Cu precipitates to be sufficiently solid-solved at the subsequent final annealing.

The conditions of the hot-rolled sheet annealing step are respectively: heating temperature: 810~1090 ° C, cooling rate: 390 ° C or less, average cooling rate: 1.1 ° C / sec or more, conditions are heating temperature: 820 ~ 1080 ° C, cooling rate: 380 Below °C, the average cooling rate: 1.2 ° C / sec or more is optimal.

As described above, the ferrite-based iron-based stainless steel sheet excellent in antibacterial property according to the first embodiment and the second embodiment and the method for producing the same can exhibit excellent antibacterial properties in the entire surface of the panel, and are excellent in high yield. Good antibacterial properties in the past. Further, according to the fat-grained iron-based stainless steel sheet of the second embodiment and the method for producing the same, the maximum concentration of Cu on the steel surface can be made highly concentrated to the extent that it is first seen, whereby better antibacterial properties can be obtained. Further, in order to achieve both antibacterial property and softening, it is preferred that the Cu content of the Cu-containing stainless steel containing stainless steel is 0.3 to 1.7%.

[Examples] (First embodiment)

The steel of the composition shown in Table 1A and Table 1B is melted by vacuum melting, and hot rolled at a heating temperature of 1100 to 1350 ° C and a final hot rolling temperature of 700 to 1020 ° C, and then a coiling temperature of 400 to 700 ° C. Take it under. Next, the hot rolled sheet was annealed at 980 ° C for 10 seconds in air, and then subjected to usual pickling. Then, cold rolling is performed to carry out final annealing, and a cold rolled sheet having a thickness of 1.0 to 1.3 mm is formed. Thereafter, it was pickled with sulfuric acid of 40 to 80 ° C and nitric acid-hydrofluoric acid to prepare a ferrite-based iron-based stainless steel plate. In addition, the field marked with "-" in Table 1A and Table 1B indicates that the element was not added and was not measured.

The following evaluations have been made regarding the obtained ferrite-based stainless steel sheets. In addition, in this embodiment, it is confirmed whether the whole domain is implemented well in the board surface. The antibacterial property was evaluated in the direction of the width of the plate covering the deviation of the antibacterial property. That is, a plurality of 50 mm square samples were cut at arbitrary points in the longitudinal direction of each steel sheet to cover the sheet width direction. Next, the entire sample was evaluated.

(Measurement of surface component concentration)

The concentration distribution of C, O, Fe, Cr, Si, Mn, Nb, Ti, Al, and Cu at a depth of about 800 nm on the steel surface was measured by glow discharge luminescence analysis (GDS). The concentrations of Cu, Fe, and Cr in the Cu-concentrated layer are exemplified in Fig. 1, and are changed in the depth direction. Next, when the concentration distribution was again calculated by excluding C, it was confirmed that the Cu concentration layer was formed on the surface of the stainless steel by changing the depth direction as shown in FIG. 2 . Further, the Cu maximum concentration of the Cu-concentrated layer was set to Cm. Further, the Fe/Cr ratio calculated from the ratio of the Fe concentration to the Cr concentration at the depth of the Cu maximum concentration Cm has also been obtained.

Further, Fig. 2 exemplifies the steel of the present invention, and the Cu maximum concentration Cm is 75.0%. Further, the Fe/Cr ratio calculated from the concentration of Fe and Cr at the position of the Cu maximum concentration Cm was 2.9.

(evaluation of antibacterial properties)

The evaluation of the antibacterial property is based on ISO 22196. 1 ml of the test bacterial solution was applied to the above sample, and allowed to stand at 25 ° C for 36 hours, and then the bacterial solution was wiped off and shaken in the diluted solution. A predetermined amount of the shaken liquid was mixed in the measurement medium, cultured at 35 ° C for 24 hours, and then the antibacterial activity value was measured. Steel having an antibacterial activity value of 2.0 or more was evaluated as a steel having excellent antibacterial properties against bacterial growth, and the evaluation of the antibacterial property in the table was indicated as "B" (Good). Moreover, when the antibacterial activity value is 4.0 or more, it is evaluated as having a characteristic For the steel with excellent antibacterial properties, the antibacterial evaluation in the table is marked "A" (Excellent). When the antibacterial activity value was less than 2.0, it was evaluated as a steel having poor antibacterial properties, and the antibacterial evaluation in the table was marked "C" (Bad).

In addition, in the table, only one numerical value is described for each steel material, but the measurement of the antibacterial property of the sample to be measured is the lowest antibacterial property, and the measurement of the surface component concentration results in the measurement of the sample having the lowest antibacterial property. result. In the case where the antibacterial activity value of the sample having the lowest antibacterial property is 2.0 or more in the sample in the width direction of each steel material, it means that the entire surface of the steel sheet has antibacterial properties.

The results of the evaluation are shown in Tables 2 to 14. Tables 2 to 7 (test Nos. 1 to 276) are the results of evaluations of the case where nitric acid-hydrofluoric acid was used as the first pickling liquid and sulfuric acid was used as the second pickling liquid in the order of pickling. Further, in Tables 8 to 14 (Test Nos. 277 to 551), in order to change the order of pickling, sulfuric acid was used as the first pickling liquid, and nitric acid-hydrofluoric acid was used as the second pickling liquid, and acid was sequentially carried out in this order. The evaluation result of the situation of washing. In addition, the fields marked with "-" in Tables 2 to 14 indicate that the processing is not performed.

The antibacterial activity value of the steel sheets of Test Nos. 1 to 180 and No. 277 to 456 of the present invention produced by the method of the present embodiment exhibited an antibacterial property of stability of 2.0 or more (antibacterial property evaluation was " B", which is the white circle in Figure 3).

Further, in Test Nos. 181 to 206 and No. 457 to 481 which were obtained by the production method of the hot rolling conditions specified by the method of the present embodiment, the maximum Cu concentration Cm exceeded 18%, and the performance was particularly excellent. Antibacterial property (antibacterial property evaluation is "A", which is the black circle of the drawing point in Fig. 3).

Further, the antibacterial activity values of the steel sheets of Test Nos. 207 to 276 and No. 482 to 551 of Comparative Examples which were produced according to the conditions of the pickling conditions specified by the method of the present embodiment were less than 2.0 (the antibacterial property evaluation was "C" is the plot point of the multiplication mark (cross mark) in Figure 3. In particular, the steel sheets of Test Nos. 207 to 221 and Test Nos. 497 to 511 were subjected to nitric acid-hydrofluoric acid treatment as the pickling treatment, so that the Cu maximum concentration Cm was less than 10%, and the antibacterial property was lower than that of the present invention.

(Second embodiment)

Hereinafter, in order to confirm the softening effect of the present embodiment, the conditions of the hot-rolled sheet annealing step and the final annealing step were changed to the conditions shown in Table 15 at the time of production of a part of the steels of Tables 1A and 1B.

Further, in the second embodiment, the hot rolling step, the cold rolling step, and the final pickling step are all carried out under the conditions within the scope of the embodiment.

The section hardness and corrosion resistance of each of the produced steel sheets have been evaluated. In addition, the section hardness was measured by the following method. Five parts were arbitrarily selected near the center of the sheet thickness, and the Vickers hardness test was performed on the selected portion, and the average value was used as the measured value of the section hardness. The corrosion resistance was measured by JIS Z2371 as a standard, and a continuous spray of 308 K, 5% NaOH for 72 hours was carried out, and the rust condition was observed.

The evaluation results are shown in Table 15.

In the example in which the preferred final annealing conditions of the present embodiment are not satisfied, the cross-sectional Hv hardness exceeds 190, or the formula (a) is not satisfied.

Further, Test Nos. 552, 555, 556, 559, 560, 563, 564, 567, 568, 571, 572, 575, 576, 579 of the present invention prepared according to the preferred final annealing conditions of the present embodiment. , 580, 583 steel plate Hv hard The degree is 190 or less, and the formula (a) is satisfied. As a result, as compared with other examples which do not conform to the preferable manufacturing conditions of the present embodiment, the point-like rust is remarkably small, and the corrosion resistance is further improved. From the above results, it is understood that, by using the preferable production conditions of the present embodiment, it is possible to produce a steel sheet which is also suitable for use in a case where softening and high corrosion resistance are required for a coin.

Industrial availability

The fat-grained iron-based stainless steel sheet of the present embodiment can exhibit excellent antibacterial properties in the entire surface of the sheet. Moreover, both softening and excellent antibacterial properties can be considered. Therefore, the ferrite-based stainless steel sheet of the present embodiment is suitable as a faucet such as a guardrail or a faucet, a metal coin, a metal container, a metal food container, a bathtub, a household appliance, a toilet, a medical appliance, a heating machine, and the like, and a building material for a building. Materials such as.

Claims (11)

An iron-based stainless steel plate having excellent antibacterial property, containing 0.1% or more and 5.0% or less by mass of Cu; and having a Cu-concentrated layer on the surface of the stainless steel plate, wherein the Cu concentration of the Cu-concentrated layer is Cm 10.0% by mass or more, and the surface of the steel sheet exhibiting the Cu maximum concentration Cm has a Fe/Cr ratio at a depth position of 2.4 or more. An iron-based stainless steel plate having excellent antibacterial property, containing 0.1% or more and 5.0% or less by mass of Cu; and having a Cu-concentrated layer on the surface of the stainless steel plate, wherein the Cu concentration of the Cu-concentrated layer is Cm 18.0% by mass or more. The ferrite-based iron-based stainless steel sheet having excellent antibacterial property as claimed in claim 1 or 2, wherein the Cu content is 0.3 to 1.7% by mass%, and the section hardness of the steel sheet is in accordance with the Vickers hardness scale, which satisfies the following ( a) Formula: Hv hardness ≦ 40 × (Cu - 0.3) + 135 (a). The ferrite-based iron-based stainless steel sheet having excellent antibacterial properties according to any one of claims 1 to 3, further comprising C: 0.050% or less, Cr: 10.0 to 30.0%, and Si: 2.00% or less, in terms of % by mass, P: 0.030% or less, S: 0.010% or less, Mn: 2.00% or less, N: 0.050% or less, and Ni: 2.0% or less, and the remainder is composed of Fe and unavoidable impurities. The ferrite-based iron-based stainless steel sheet having the excellent antibacterial property of claim 4 further contains one or both of Ti: 0.50% or less and Nb: 1.00% or less in terms of % by mass. An iron-based stainless steel plate having excellent antibacterial properties as claimed in claim 4 or 5, Further, it may further contain one or more selected from the group consisting of Sn: 1.00% or less, Mo: 1.00% or less, Al: 1.000% or less, Mg: 0.010% or less, Co: 1.000% or less, and V: 0.50%. Hereinafter, Zr: 0.10% or less, REM: 0.100% or less, La: 0.100% or less, B: 0.0100% or less, and Ca: 0.010% or less. A ferrite-based iron-based stainless steel sheet having excellent antibacterial properties as claimed in any one of claims 1 to 6, which is used for a metal coin. A method for producing a fermented iron-based stainless steel sheet having excellent antibacterial properties, comprising a hot rolling step, a cold rolling step and a final pickling step; the stainless steel sheet having the composition of any one of claims 1 to 6; The pickling step comprises the steps of: immersing in a 5.0 to 35.0% by mass aqueous sulfuric acid solution in the first pickling step; and immersing in 1.0 to 15.0% by mass of nitric acid and 0.5 to 5.0% by mass in the second pickling step. In the acid solution of the hydrofluoric acid aqueous solution. The method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial property according to claim 8, wherein the hot rolling step is performed under the conditions of a heating temperature of 1150 to 1300 ° C, a final temperature of 800 to 1000 ° C, and a coiling temperature of 600 ° C or less. get on. A method for producing a ferrite-based iron-based stainless steel sheet having excellent antibacterial properties according to claim 8 or 9, further comprising a hot-rolled sheet annealing step and a final annealing step; wherein the stainless steel sheet has any one of claims 3 to 6 ingredient And the foregoing final annealing step comprises the steps of: annealing at an annealing temperature of 900 to 1100 ° C; and cooling to 400 ° C at an average cooling rate of 3 ° C /sec or more. The method for producing a ferrite-grained stainless steel sheet having excellent antibacterial property according to claim 10, wherein the annealing step of the hot-rolled sheet is performed by continuous annealing, and the continuous annealing comprises annealing at an annealing temperature of 800 to 1100 ° C. Step; secondly, the step of cooling to 400 ° C at an average cooling rate of 1 ° C /sec or more.